LAN - Local Area Network

A LAN describes a network that is “local” to a home, office or campus. It may be as simple as a single Ethernet Switch, or it may contain hundreds of switches connected together using copper and fibre cabling. Typically it will be a self-contained network, which is often sub-divided into LAN segments to reduce and contain the local area traffic. Virtual LANs (VANs) may be used to assist with local area segmentation and security, and WAN links are used to connect to remote locations.

Ethernet Switch

When LANs were first invented, a Hub was used to join network segments together, but Hubs had the disadvantage in that they broadcast all the network traffic over the whole network. An ethernet SWITCH is an intelligent hub which learns which devices are connected to which ports (using MAC address learning techniques) and can contain traffic to the local ports which need to know. This greatly reduces network traffic and eliminates network overload.

VLAN

A Virtual LAN is a technology which further segments a local area network by allow the network administrator to group together different types of network user. For example, the Finance, Sales and Logistics departments within a company can all operate on their own unique VLAN. This means that all finance network traffic is contained within the Finance VLAN, and the same is true for the Sales and Logistics traffic. This can greatly reduce the amount of network traffic, giving greater bandwidth to the individual departments. Only traffic which needs to traverse the VLAN boundaries is permitted outside the VLAN, and routing mechanisms (built into the Ethernet Switches) are used to police the inter-VLAN traffic, which allows all sorts of security checks to be implemented if required.

WAN

A Wide Area Network describes a network “outside” the LAN. For example, a WAN is the link that connects your head office LAN in London to your Branch office LAN in Leeds. It also includes the network that links your “private” office LAN to the “public” Internet and World Wide Web. Older WAN links often used leased lines provided by BT and other network carriers, but nowadays WAN links are typically “supported” by the global Internet network – see VPNs. Many new techniques are available to improve the throughput of WAN links which are inherently slow, compared to LAN network speeds.

VPN

A Virtual Private Network describes a network that typically runs over a “public” network (e.g. the Internet) but provides a secure and private link. A good example is a business which has a head office and a branch office in two locations, and which uses the “public” Internet to exchange data between the sites. By setting up a VPN, the data can be kept secure and private by using advanced encryption techniques and user keys.

WAN Acceleration

WAN links are inherently slow, compared with LANs, because of the distance that they cover. Just think of the old dial-up (POTS) links that were used in the 1990s to connect to the Internet from home, or the 2Mpbs leased lines provided by BT. Even today’s WAN links typically only support 8 or 16 mbps, which are slow compared with the gigabit and 10-gigabit speeds achieved on a LAN. More and more companies are placing their applications in one office, and requiring access to these applications from other branch offices. A traditional WAN link will not support the level of network traffic generated, but by employing WAN acceleration many users can be supported. WAN acceleration products include ingenious data compression and data caching.

Network Speeds

Network speeds are measured in Bits Per Second (BPS) or Mega (or 1,000,000) Bits Per Second (MPBS). The original Local Area Networks operated at 10mbps, but most LANs now operate at 100mbps and 1000mbps (or Gigabit), with the latest devices offering 10-Gigabit. Fibre cabling offers the fastest speeds over longer distances – see Copper and Fibre below.

Copper and Fibre Cabling

Nearly all local area networks today employ copper and fibre cabling. Twisted pair copper cabling, also known by the style of connector used (RJ45) or the quality of the cable (Cat 5, Cat6, Cat6e), is restricted to 100 metre lengths between devices. Local area links which exceed these distances will use either Multimode or Singlemode fibre cabling. Multimode fibre is used for the short to mid lengths (e.g. up to 2km depending on speed) and Singlemode is used for longer distances up to 20km.

Layer 3/4 Switching

As technology advances, more and more intelligence being deployed in Ethernet switches. Originally, an Ethernet switch simply “switched” the network traffic between its ports dependant on the Layer 2 MAC address in the network packet header. Now, more sophisticated switches include Layer 3 Routing functions and Layer 4 features such as Quality of Service. All of these advanced technologies help to minimize network traffic and improve security as the network has to support more and more bandwidth hungry applications like video, voice and TV.

Wireless

A wireless network does what is says – it provides a link between computer devices (e.g. PCs, Routers, Printers) WITHOUT using wires or cables. In the early days of wireless networks, the technology was considered too insecure and open to hackers. But with improved security techniques (e.g. WEP, LEAP, Encryption) a wireless network is now considered almost as safe as a wired/cabled network, providing all the security features are employed. Typical wireless speeds are still slow (108mbps) compared with a cabled networks (1000mbps), but the advantages of easy and flexible deployment often outweigh the speed disadvantages.

Peer to Peer Network

A network of personal computers, each of which acts as both client and sever, so that each can exchange files and email directly with every other computer on the network. Each computer can access any of the others, although access can be restricted to those files that a computer's user chooses to make available. Peer-to-peer networks are less expensive than client/server networks but less efficient when large amounts of data need to be exchanged.

Client/Server Network

A computer network in which one centralized, powerful computer (called the server) is a hub to which many less powerful personal computers or workstations (called clients) are connected. The clients run programs and access data that are stored on the server.

Intranet

A privately maintained computer network that can be accessed only by authorised persons, especially members or employees of the organization that owns it.

Extranet

An extension of an institution's intranet, especially over the World Wide Web, enabling communication between the institution and people it deals with, often by providing limited access to its intranet.

Private internet address

Private networks are becoming more common in office local area network (LAN) designs, as many organisations do not see a need for globally unique IP addresses for every computer, printer and other device that the organisations use. Another reason for the extensive use of private addresses is the shortage of publicly registered IP addresses.